Low pressure oxo hydroformylation of an olefin with carbon monoxide and hydrogen in the presence of a rhodium complex catalyst to produce aldehydes is now well known in the art.
For instance, U.S. Pat. No. 3,527,809, the entire disclosure of which is incorporated herein by reference thereto, discloses a hydroformylation process where olefins are hydroformylated with carbon monoxide and hydrogen in the presence of a rhodium complex catalyst and free triarylphosphine to produce aldehydes in high yields at low temperatures and pressures, where the normal to iso-(or branch chain) aldehyde isomer ratio of product aldehydes is high.
It is also known that, under hydroformylation conditions, some of the product aldehydes may condense to form by-product, high boiling aldehyde condensation products such as aldehyde dimers or trimers. Commonly-assigned U.S. Pat. No. 4,148,830, the entire disclosure of which is incorporated herein by reference thereto, disclosed the use of these high boiling liquid aldehyde condensation products as a reaction solvent for the catalyst.
In addition commonly-assigned copending U.S. Application Ser. No. 776,934, filed Mar. 11, 1977, U.S. Pat. No. 4,247,486 (Belgium Pat. No. 853,377), the entire disclosure of which is incorporated herein by reference thereto, discloses a liquid phase hydroformylation reaction using a rhodium complex catalyst, wherein the aldehyde reaction products and some of their higher boiling condensation products are removed in vapor form from the catalyst containing liquid body (or solution) at the reaction temperature and pressure. The aldehyde reaction products and the condensation products are condensed out of the off gas from the reaction vessel in a product recovery zone and the unreacted starting materials (e.g., carbon monoxide, hydrogen and/or alpha-olefin) in the vapor phase from the product recovery zone are recycled to the reaction zone. Furthermore, by recycling gas from the product recovery zone coupled with make-up starting materials to the reaction zone in sufficient amounts, it is possible, using a C.sub.2 to C.sub.5 olefin as the alpha-olefin starting material, to achieve a mass balance in the liquid body in the reactor and thereby remove from the reaction zone at a rate at least as great as their rate of formation essentially all the higher boiling condensation products resulting from self-condensation of the aldehyde product.
It is also known in the prior art that even in the absence of intrinsic poisons there may be deactivation of rhodium hydroformylation catalysts under hydroformylation conditions. Copending, commonly-assigned U.S. patent Application Ser. No. 762,336 filed Jan. 25, 1977, abandoned in favor of continuation U.S. App. Ser. No. 151,293, now U.S. Pat. No. 4,260,828, (Belgium Pat. No. 863,268), the entire disclosure of which is incorporated herein by reference thereto, indicates that the deactivation of rhodium hydroformylation catalysts under hydroformylation conditions in the substantial absence of extrinsic poisons is due to the combination of the effects of temperature, phosphine ligand: rhodium mole ratio, and the partial pressures of hydrogen and carbon monoxide and is termed an intrinsic deactivation. It is further disclosed therein that this intrinsic deactivation can be reduced or substantially prevented by establishing and controlling and correlating the hydroformylation reaction conditions to a low temperature, low carbon monoxide partial pressure and high free triarylphosphine ligand: catalytically active rhodium mole ratio.
It has also been observed that the presence of an alkyldiarylphosphine (for example, propyldiphenylphosphine or ethyldiphenylphosphine) in the rhodium-catalyzed hydroformylation of the alpha-olefin propylene inhibits catalyst productivity; i.e., the rate at which the desired product aldehydes are formed. Specifically, the addition of small amounts of propyldiphenylphosphine or ethyldiphenylphosphine to rhodium hydroformylation solutions markedly reduced the rate of production of butyraldehydes from propylene, compared to the rate obtained in the absence of the alkyldiarylphosphines.
Although the presence of alkyldiarylphosphines in rhodium-catalyzed hydroformylation processes reduces the catalyst productivity, the stability of such rhodium complex catalysts can be enhanced by providing an alkyldiarylphosphine in the reaction medium and copending, commonly assigned U.S. Application Ser. No. 762,335 filed Jan. 25, 1977 abandoned in favor of continuation U.S. App. Ser. No. 140,830, (Belgium Pat. No. 863,267), the entire disclosure of which is incorporated herein by reference thereto, teaches that the reaction conditions can be adjusted to be more severe in order to regain this apparent loss of catalyst productivity while retaining the enhanced catalyst stability.
Thus, it is known that, despite the obvious advantages of the above inventions, during use the rhodium complex catalyst loses activity (i.e. becomes partially deactivated) and eventually, after prolonged use, the activity of the catalyst will have decreased to such a point that it is no longer economically desirable to operate the hydroformylation process and the catalyst will have to be discharged and replaced with fresh catalyst. Accordingly, the discovery of new rhodium catalysts which may prove to be more robust than conventional rhodium-based catalysts in that they may be able to better withstand more severe reaction conditions and/or separation conditions than currently being practiced is of no small importance to the state of the art.